Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session K46: Advances in Scanning Probe Microscopy III: Scanning Probe Spectroscopic TechniquesFocus
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Sponsoring Units: GIMS Chair: Jeonghoon Ha, National Magnet Laboratory Room: 311 |
Wednesday, March 16, 2016 8:00AM - 8:12AM |
K46.00001: The influence of deformation rate on polymer nanomechanical properties as measured by Atomic Force Microscopy. Bede Pittenger, Thomas Mueller Polymeric composites often have heterogeneities at the nanometer length scale. AFM based mechanical property measurements have the sensitivity and resolution necessary to visualize these features and better understand their influence on bulk properties. In the past few years, AFM mechanical property mapping has evolved from slow force volume to faster, but conceptually very similar, PeakForce Tapping. Currently, the time scale of tip-sample interaction spans from microseconds to seconds, tip sample forces can be controlled from piconewtons to micronewtons, and spatial resolution can reach sub-nanometer. AFM has become a unique mechanical measurement tool having large dynamic range (1kPa to \textgreater 100GPa in modulus) with the flexibility to integrate with other physical property characterization techniques in versatile environments. In particular, researchers have begun to take advantage of the wide range of deformation rates accessible to AFM in order to study time dependent properties of materials such as viscoelasticity. This presentation will review this recent progress, providing examples that demonstrate the dynamic range of the measurements and the resolution with which they were obtained. Additionally, the effect of time dependent material properties on the types of measurements will be explored. [Preview Abstract] |
Wednesday, March 16, 2016 8:12AM - 8:24AM |
K46.00002: Atomic Force Tomography of a Nonplanar Molecule: Role of Lateral and Chemical Sample-Tip Interactions Xianghua Kong, Wei Ji Atomically identification of the molecular geometric structures is an important prerequisite to understand their chemical and electrical properties. TiOPc, a steric structure, gives rise to two adsorption configurations of TiOPc on Cu(111), namely O-dn and O-up. The roles of chemical specific interactions of different intramolecular atoms with the AFM tips were discussed at the submolecular level. For O-up, the molecular backbone of TiOPc is only visible out of a certain range from the center of the molecule, accompanied with significant dissipation signal. Theoretical calculation identifies such dissipation signal as the chemical attraction between the out-of-plane O in TiOPc and the Cu atoms behind the CO of a tip at a certain range of lateral distance between them. When they approach closer, the sample O repulses another O in the CO tip making it tilting strongly, which softens the tip and thus leads to even stronger O (sample) -- Cu (tip) attraction. A direct demonstration of sample-tip electronic hybridization was manifested in the simpler O-dn case where an explicit wavefunction overlap between the tip O atom and the sample Ti atom. Given these results presented here, we anticipate that this method might be developed further generally useful in single-molecule chemistry and physics. [Preview Abstract] |
Wednesday, March 16, 2016 8:24AM - 8:36AM |
K46.00003: Scanning Ion Conductance Microscopy for living cell membrane potential measurement Namuna Panday Recently, the existence of multiple micro-domains of extracellular potential around individual cells have been revealed by voltage reporter dye using fluorescence microscopy. One hypothesis is that these long lasting potential patterns play a vital role in regulating important cell activities such as embryonic patterning, regenerative repair and reduction of cancerous disorganization. We used multifunctional Scanning Ion Conductance Microscopy (SICM) to study these extracellular potential patterns of single cell with higher spatial resolution. To validate this novel technique, we compared the extracellular potential distribution on the fixed HeLa cell surface and Polydimethylsiloxane (PDMS) surface and found significant difference. We then measured the extracellular potential distributions of living melanocytes and melanoma cells and found both the mean magnitude and spatial variation of extracellular potential of the melanoma cells are bigger than those of melanocytes. As compared to the voltage reporter dye based fluorescence microscope method, SICM can achieve quantitative potential measurements of non-labeled living cell membranes with higher spatial resolution. [Preview Abstract] |
Wednesday, March 16, 2016 8:36AM - 8:48AM |
K46.00004: Local Imaging of Conductance Evolution in Ion-Gel-Gated Transitional Metal Dichalcoginide Transistors Xiaoyu Wu, Di Wu, Hongtao Yuan, Harold Hwang, Yi Cui, Keji Lai Electrolyte-gated electric double layer transistors (EDLTs) have demonstrated carrier density modulation in a remarkably wide range in systems ranging from complex oxides to layered metal chalcoginides. Cryogenic microwave impedance microscopy (MIM) has been used to perform real-space mapping of nanoscale conductance evolution in oxide EDLT gated with an ultrathin ionic gel layer. However, such microwave imaging was previously only possible at temperatures lower than the glass transition temperature (frozen temperature) of the gel because of the contact-mode scanning. Here, we report in-situ imaging of conductance evolution in WSe$_{\mathrm{2}}$ transistors using a MIM based on the frequency-modulated atomic force microscopy (FM-AFM) mode. With a typical tip-sample distance of 30nm, the WSe$_{\mathrm{2}}$ EDLT can be simultaneously gate-modulated and imaged at 220K, which is above the frozen temperature of the gel. The microwave images vividly show the spatial evolution of channel conductance in WSe$_{\mathrm{2}}$ during the metal-insulator transition and mesoscopic electronic inhomogeneity with different configurations of source/drain/gate voltages. Such in-situ microwave imaging provides new opportunities to correlate the macroscopic transport results and microscopic conductivity distribution in both equilibrium and non-equilibrium states of the EDLTs. [Preview Abstract] |
Wednesday, March 16, 2016 8:48AM - 9:00AM |
K46.00005: Resolving local voltage variations in opto-electronic devices with Kelvin probe force microscopy Elizabeth Tennyson, Joseph Garrett, Jeremy Munday, Marina Leite We employ illuminated Kelvin probe force microscopy (KPFM) to spatially resolve the open-circuit voltage ($V_{oc})$ of optoelectronic devices with nanoscale spatial resolution, \textgreater 5 orders of magnitude better than previous methods. In illuminated-KPFM, we measure the difference in work function between the sample surface and the probe, termed the contact potential difference (CPD). By grounding the bottom contact of the solar cell to the AFM probe, the difference between the illuminated and the dark signals is proportional to quasi-Fermi level splitting and, therefore, the $V_{oc}$. We apply our scanning probe technique to a variety of solar cell materials, including polycrystalline CIGS, where we resolve local variations in $V_{oc}$ \textgreater 150 mV [1]. We use heterodyne-KPFM (where we map 1 $\mu $m$^{\mathrm{2}}$ in 16 seconds) to probe hybrid perovskites solar cells, and quantify in real-time the voltage changes upon material relaxation after illumination. This metrology yields new insights into the local electrical properties of solar cells, and can be expanded to any optoelectronic device. [1] E.M. Tennyson et al., Adv. Energy Mat., \textbf{5} (2015) in press, front cover. [Preview Abstract] |
Wednesday, March 16, 2016 9:00AM - 9:12AM |
K46.00006: Multi-step atomic interchange mechanism for atom manipulation on semiconductor surfaces. Batnyam Enkhtaivan, Atsushi Oshiyama We report on our total-energy electronic-structure calculations based on the density-functional theory that clarify atom-scale mechanisms of atom-manipulation recently realized on semiconductor surfaces [1]. We focus on Ge(111) and Si(111) surfaces and identify reaction pathways and corresponding reaction energy barriers. Considering the atom manipulation of Pb and Sn atoms on Ge(111) surfaces, we find that the substitutional Sn (Pb) diffuses to neighboring Ge adatom, and forms a dimer with Ge spontaneously. Then the Sn (Pb) and the Ge adatom exchange their position concertedly with the dimer structure kept. These diffusion and exchange processes are multi-step atomic processes consisting of multiple metastable states. For the case of Sb manipulation on the Si(111) surface, the dimer structure does not form spontaneously when the AFM tip is absent. We find that the roles of the AFM tip during the atom manipulation are the lowering of the diffusion energy barrier and stabilization of the dimer structure. [1] Y. Sugimoto et al., e-J. Surf. Sci. Nanotech. 4, 376-383 (2006). [Preview Abstract] |
Wednesday, March 16, 2016 9:12AM - 9:48AM |
K46.00007: Measuring electron-phonon coupling with Scanning Tunneling Microscopy Invited Speaker: Vidya Madhavan Electron-boson interactions are~ubiquitous in systems ranging from simple metals to novel materials such as graphene, high-temperature superconductors and topological insulators. Of particular interest is the coupling between electrons and phonons. In general, electron-phonon coupling gives rise to quasiparticles of decreased mobility and increased effective mass. Nearly all information about electron-phonon coupling is contained in the Eliashberg function ($\alpha^{2}F(\omega ;k,E)) $of the material. In this talk I discuss the various methods by which the effects of electron-phonon coupling can be measured by scanning tunneling microscopy. I will present STM data on a variety of systems ranging from metals to topological insulators and discuss the signatures of electron-phonon interactions in different types of STM data. In particular I discuss how high resolution measurements allow us to measure the dispersion and obtain the real part of the self-energy, which can in principle be inverted to obtain the Eliashberg function. [Preview Abstract] |
Wednesday, March 16, 2016 9:48AM - 10:00AM |
K46.00008: Lateral manipulation and interplay of local Kondo resonances in a two-impurity Kondo system. Haiming Guo The control of a single spin of an atom is of great interest in Kondo physics and a potential application in spin based electronics. Low-temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS) is a powerful tool to probe the single spin and its Kondo effect at the atomic scale on surfaces. I am going to present the modulation of magnetic properties and Kondo effect of Co adatoms on graphene layer. This is also the first discovery of a Kondo effect caused from a magnetic impurities doped in graphene layer in experiment. The tiny diverse interaction between magnetic impurity and graphene host further modulates the Kondo effect. Next, the atomic-scale spatial relationship of a two-impurity Kondo system at varying lateral distance will be reported. A notable interplay is determined between two individual Kondo singlet states, which are formed by the localized spins of two cobalt magnetic adatoms that are placed on different electrodes of an STM. The \textit{dI/dV} spectra show the continuous changes of the resonance peak feature when approaching the Kondo tip laterally to the local sample-Kondo impurity on the surface. [Preview Abstract] |
Wednesday, March 16, 2016 10:00AM - 10:12AM |
K46.00009: Local Force Interactions and Image Contrast Reversal on Graphite Observed with Noncontact Atomic Force Microscopy Omur Dagdeviren, Jan Goetzen, Eric Altman, Udo Schwarz Surface interactions of graphene-based nanostructures remain a topic of considerable interest in nanotechnology. Similarly, tip-dependent imaging contrasts have attracted attention as they allow conclusions to be made about the surface's chemical structure and local reactivity. In this talk, we present noncontact atomic force microscopy data recorded in the attractive regime on highly oriented pyrolytic graphite that reveals image contrast reversal for the first time. While larger tip-sample separations feature bright spots on atomic sites, the maximum of the tip-sample interaction flips to the hollow site positions upon further approach, which represents the contrast predominantly observed in previous studies during attractive-mode imaging. This cross over of the local chemical interaction is confirmed in force spectroscopy experiments. The results will be discussed in light of recent theoretical simulations that have predicted the occurrence of such contrast reversal for specific tip terminations. [Preview Abstract] |
Wednesday, March 16, 2016 10:12AM - 10:24AM |
K46.00010: \textbf{Theoretical model of the tunneling current between a metallic tip and a ferroelectric material.} Ravi Neupane, Andrew Yost, TeYu Chien We present a model to calculate the tunneling current for a ferroelectric (FE) material in a metal/vacuum/Ferroelectric tunneling junction. Using this model, we try to explore the effect of the FE dipole orientation's direction on $I-V $spectrum using scanning tunneling spectroscopy (STS). The STM tunneling current for non-FE materials depends upon various factors such as tip -sample distance (vacuum gap), temperature, density of states (DOS) of tip and of sample, and tip-sample bias. FE materials have internal electric dipoles giving rise to internal and external electric fields. The electric field induced by these dipoles will distort the fermi level as a function of depth in the material. In our model, the Fermi level is assumed to be inclined with a slope as a function of the depth. The slope depends upon the orientation and the strength of the electric dipole moment. In this model we use the WKB method accounting for the slope of the fermi level to calculate the tunneling probability from tip to different depths then summing all contributions to obtain the total current as a function of tip-sample bias, i.e. $I-V $curves. [Preview Abstract] |
Wednesday, March 16, 2016 10:24AM - 10:36AM |
K46.00011: The power laws of nanoscale forces in ambient conditions Matteo Chiesa, Sergio Santos, Chia-Yun Lai Power laws are ubiquitous in the physical sciences and indispensable to qualitatively and quantitatively describe physical phenomena. A nanoscale force law that accurately describes the phenomena observed in ambient conditions at several nm or fractions of a nm above a surface however is still lacking. Here we report a power law derived from experimental data and describing the interaction between an atomic force microscope AFM tip modelled as a sphere and a surface in ambient conditions. By employing a graphite surface as a model system the resulting effective power is found to be a function of the tip radius and the distance. The data suggest a nano to mesoscale transition in the power law that results in relative agreement with the distance-dependencies predicted by the Hamaker and Lifshitz theories for van der Waals forces for the larger tip radii only [Preview Abstract] |
Wednesday, March 16, 2016 10:36AM - 10:48AM |
K46.00012: Development of tip Scanning High Speed AFM operating at 1,000 Lines/s {\&} 15\textmu m Umit Celik, Ihsan Kehribar, Kubra Celik, H. Özgür Özer, Ahmet Oral High speed atomic force microscope allows imaging dynamic processes on the surfaces. We have developed a very high speed tip scanning atomic force microscope (HS-AFM). We designed the tip scanning system to overcome the sample size limits, with a beam tracking capability to follow the cantilever motion. A high resonance frequency flexure scanner developed which has 15\textmu m scan range in XY and 3\textmu m in Z axis. A novel FPGA based high speed scanning and data acquisition system was developed. The scanner is driven by sine wave in X-axis to avoid resonances and data were captured at equal sample intervals. 1 KHz line scan rate is achieved at 15\textmu m scan range with the HS-AFM. [Preview Abstract] |
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